This invention relates to a scanning confocal optical device, which focuses a beam of light emitted from a substantial point light source on a specimen surface and scans the focused beam of light so as to detect light reflected therefrom or fluorescence therefrom.
These days, scanning confocal optical devices are known as means for making a close observation of the surface or the interior of living tissue or a cell. Such confocal optical devices are advantageous in that they have a resolution that exceeds the resolution limit of conventional optical devices and can form a three-dimensional image. However, conventional confocal optical devices have a large optical system and hence are hard to insert into a body. Accordingly, living tissue is usually removed from the body and then observed.
To overcome the above drawback, an optical system for use in a fine scanning confocal optical device is disclosed, as an example aiming at miniaturization of optical systems, in the article "Micromachined scanning confocal optical microscope" in OPTIC LETTERS, Vol. 21, No. 10, May, 1996, or in U.S. Pat. No. 5,742,419.
As is shown in FIG. 4, the disclosed fine scanning confocal optical device comprises a light source 1, a light transmitting section 2, a light detecting section 3, a light scanning section 4 and a processing section 5. The light transmitting section 2 has a single-mode fiber, which allows the light scanning section 4 to be inserted into the body through an endoscope, so that the device suggests the possibility of the formation of a three-dimensional image of the interior of a body in a real-time manner.
FIG. 5 shows the structure of the light scanning section 4. A laser beam, which is emitted from the light source 1 and transmitted through a single-mode fiber 10 in the light transmitting section 2, is reflected by a reflective surface 11, then deflected in an X direction by an electrostatic mirror 12 for X-directional scanning, totally reflected by a reflective section 14, deflected in a Y direction by an electrostatic mirror 13 for Y-directional scanning, and focused on a specimen surface 16 by a diffractive lens 15.
The end face of the single-mode fiber 10 and the specimen surface 16 are in a conjugate relationship, and light reflected from the specimen surface 16 returns through the above-mentioned optical path, thereby converging onto the end face of the fiber 10. In other words, light reflected from the specimen surface 16 enters the diffractive lens 15, then is reflected by the electrostatic mirror 13, the reflective section 14, the electrostatic mirror 12 and the reflective surface 11 in this order, and converges onto the end face of the single-mode fiber 10 as a result of the converging function of the diffractive lens 15. Light converging on the single-mode fiber 10 is transmitted therethrough in the light transmitting section 2, and then detected by the light detecting section 3.
In the above optical system, the core of the end face of the single-mode fiber serves as a pinhole, which makes the system function as a confocal optical system. Accordingly, scattered light from a place other than a focus point on the specimen surface 16 is sufficiently weak and is not actually detected by the light detecting section 3.
By virtue of the above, the optical system has a higher resolution, than that of the conventional optical systems, both in lateral directions (X and Y directions) of the specimen surface 16 and in the depth direction (Z direction) of the surface 16. Thus, the above optical system has a higher widthwise resolving power and lengthwise resolving power than those of the conventionally used optical systems.
The above-described fine scanning confocal optical device has a lower resolving power than that of the conventional confocal optical devices. However, this resolving power is sufficient to observe, for example, the bowels, although the device has a very small size.
The above fine scanning confocal optical device is of a so-called lateral-sight type, in which the field of view is perpendicular to the longitudinal direction of the probe. On the other hand, general endoscopes are of a direct-sight type, in which their insertion direction is identical to the direction of the field of view. When using the lateral-sight type confocal optical device through a channel of the direct-sight type endoscope, it is difficult to determine the observation range of the device.
In light of the easiness of determination of the observation range or in light of the operability, a direct-sight type confocal optical device, in which its longitudinal direction is identical to the direction of the field of view, is suitable for the direct-sight type endoscope.
Moreover, an object such as a living body has a low reflectance, and accordingly a signal reflected from the living body has a very low level. In an optical system directed to a living body as an object, it is important to suppress, as much as possible, a noise component reflected from a lens surface, a reflective surface, etc. of the system without reaching the object.